According to theusers' information leaflet, Nitrofurantoin (also known as Macrobid, Macrodantin or Genfura) is used 1) to cureurinary infections and 2) to prevent them. It is proved below that if used to prevent urinary infections, in mycase it also prevented catheterblockages. I do not know for how manyother people with catheter blockages it would be effective. It would be unlikely to work for those whohave blockages caused by kidney stones or bladder stones.
The normal dose forpreventing urinary infections is 50 or 100mg daily at night. Having taken 50mg per day for 30 days, thiswas reduced to 50mg 3 or 4 times per week and then to just nights when I wasfeeling feverish as might warn of a urinary infection or when there was aconsiderable amount of sediment in my catheter. That worked for me, but others might needdifferent doses. Like other medications,Nitrofurantoin comes with many cautions and possible side-effects, listed in theusers' information leaflet, but I have not had any at these doses.
As well as takingNitrofurantoin I also repositioned my catheter by pulling it forwardimmediately after going to bed to prevent the intake being obstructed bypressing up against my bladder wall and, as far as possible, assisted drainageby gravity by placing my catheter flat on the bed rather than strapped to myleg.
I have also usedseveral supporting methods to keep my catheter clear. These are listed below.


From January to July 2016the misery of my spinal injury was aggravated by the torment of catheter blockages. Here are a few observations to help identifywhat had been causing them:

1 My suprapubiccatheter was installed in May 2013, about 4 months after my spinal injury. Ihad no blockage during the first two years and eight months but I had 23between 17/1/16 and 24/7/16. Towards the end of that period, they becamemore frequent.

2 All the blockages occurred soon after changing positions from sitting uprightin my wheelchair to lying flat on my back in bed. On every occasion Ihave wakened up sweating and trembling with exceptionally violent spasms, usuallybetween midnight and 1am. There is ahighly significant relationship between time and occurrence of blockages. If we use simple dichotomy that blockages could occur at either day or night, ifthere were no relationship between time of blockage and occurrence, theprobability of any one blockage occurring at night would be 0.5. The probability of all 23 blockages occurringat night would be 0.523 = 0.000000119 or a little over 1 chance inten million.
The base is 0.5 and theexponent is 23.
The binomial distribution can also be used with the sameresult:

where N = 23, k = 23, p = 0.5 and the answer is p(k outof N)

The multinomial distribution can be used too:
where the number ofoutcomes is 2 (night/day), the number of occurrences 23 and 0, p = 0.5 for eachoutcome.
Sitting is a wheelchair,my catheter is usually strapped to the upper side of my left leg. If left there when lying flat in bed, thispart of my catheter might be at a higher level than the intake, impeding flowby gravity. I have noticed that sweatinghas on a few occasions been stopped by unstrapping my catheter from my leg andlaying it at a lower level on the bed. Now I always have it unstrapped when in bed.

3 Thenurse has never taken more than a few minutes to unblock the obstruction. It takes about 10 minutes for the sweatingand spasms to subside enough to be clearly noticeable and a further 10 minutesfor the sweating to have gone and the spasms returned to their normal level. In perhaps 8 or 10 of my 23 cases of blockage,it was uncertain why the blockage had cleared. Sometimes there was insufficient sediment for that to be a likely cause. Movement of the catheter in some cases seemedto be sufficient to make the urine to flow. Unblocking the catheter did not in every case cause a sudden, clearlyvisible flow of urine.

4 Onlyonce has a blockage recurred during the same night. On this occasion, twonurses arrived at 10.50pm and replaced my catheter which was choked with'sludge'. At 2.40am I woke sweating again. The same nursesreturned. This time the blockage was 'positional'.

5 There were at least two causes of the blockages - bacterial and physicalobstruction.


6 For abouthalf of the blockages, the nurse mentioned sediment and/or 'pus' as the likelycause. On some occasions, including the most recent, only 36 hours aftera bladder wash-out, the nurse said there was no sediment.

7 My leg bagis supposed to be changed weekly. On 3 or 4 occasions, the nurse hasmentioned a dirty leg bag, when the carers (and me) had forgotten about it orwhen we had run out of them.

8 Onthe morning following several of the blockages I have had a bout of sweatingwhich has always been stopped by taking Nitrofurantoin. This seems toindicate that I had a urinary infection, and that the infection was caused bybacteria which also caused the blockage the night before. A urine sample has never beentaken at the time of a blockage or soon after. However, it seems likely that the bacteria killed by Nitrofurantoincreated the sediment which resulted in most of the blockages.
I do not have a goodexplanation as to why I had no blockages between installation of my catheter inMay 2013 and 17/1/16 despite having more than a dozen urinary infections duringthis period. I can only state theobvious that whatever bacteria were causing these infections did not producesufficient sediment to cause a blockage but there was a change in January2016. Before July 2016 I tookNitrofurantoin only occasionally to cure urinary infections.
When Nitrofurantoin stoppedmy blockages it also removed the additional spasms accompanying the infectionand the blockage. So Nitrofurantoin achievefour results for me: i) it cured urinary infections; ii) it prevented urinary infections; iii) it preventedblockages; iv) it cured/prevented additional spasms resulting from infectionsand blockages.


9 Weeklybladder wash-outs were started soon after the blockages began. I havenever had a blockage on the following night, but I have had them soonafter.

10 Forabout half the blockages, the nurse mentioned a physical obstruction, such as acollapsed tube. I do not know why physical obstructions were absent fromMay 2013 until January 2016. Maybe there was a change in type orbrand of catheter in December 2015 or January 2016?

11 Forthe most recent blockage, the nurse offered the following explanation: theend of the catheter tube might be pressing up against my bladder wall, soobstructing the intake. This fits well with what two or three othernurses have said: 'I'm not sure what caused the blockage but wiggling thecatheter where it enters the bladder seemed to unblock it'.

From 17/1/16 to 24/7/16 Ihad 23 blockages, including 6 from 15 - 24/7/16. It seemed thatinfections by bacteria were responsible for the majority of the blockages(point 8 above) and the position of my catheter for the others (point11). It is likely that someblockages were caused by a combination of the two: a constriction not severeenough to block the flow of urine caused sediment to collect on the upstreamside and this caused a blockage.
So it is very likely thatchanging positions from wheelchair to bed triggered nearly all the blockages,most of which were caused by sediment in the catheter. Why might changing positions cause anaccumulation of sediment in my catheter? Gravity would probably act more weakly in bed; sediment in my bladdermight change position on going to bed and obstruct the intake of my catheter. These are possible explanations as to whychanging positions from wheelchair to lying flat in bed seemed to triggerblockages but I do not have a convincing answer.
Since 24/7/16 I have taken 50mgNitrofurantoin each day at about 8pm to allow time for it to take effectbefore moving from wheelchair to bed (point 8) and pulled my catheterforward away from the bladder wall immediately after going to bed (point11). From 24/7/16 - 12/8/16 I had no blockage in 20 nights.

So WITHOUT Nitrofurantoinand catheter repositioning: 10 nights, 6 blockages;
WITH Nitrofurantoin and catheter repositioning: 20nights, no blockage.

It looks obvious that there is a connection betweenNitrofurantion/catheter repositioning and stopping blockages. The strength of the evidence can be measuredlike this:

what are the chances of having 6 blockages on the first 10nights (without Nitrofurantoin) and none on the following 20 (withNitrofurantoin) if Nitrofurantoin and catheter repositioning had no effect?

That can be calculated like this:

if there had been just one blockage, the chances of itbeing in the first 10 nights would have been 10 divided by the total number ofnights (30) = 0.3333;

if there had been two blockages the chances of both of thembeing in the first 10 nights would have been 0.3333 multiplied by 0.3333 =0.1111 and so on ...... until

the chances of 6 blockages all being in the first 10 nightsis 0.3333 multiplied by itself five times or 0.33336 = 0.0014, thatis 14 chances in 10,000 or 1 chance in 714 (10,000 is the number that 0.0014would have to be multiplied by to get 14). So the probability of there being no association between takingNitrofurantoin/catheter repositioning is low, therefore the probability thatthere is an association is high. It is 1- p = 0.9986 = 9,986 chances in 10,000 =9,986/(10,000 - 9,986) chances in 10,000/(10,000-9,986) = 713 chances in 714.

The probability of there being no association betweentaking Nitrofurantoin/catheter repositioning and the occurrence of catheterblockages can also be calculated using the binomial distribution where theprobability of success for a single trial is again 10/30 = 0.3333, the numberof trials is 6 (the number of blockages on all 30 nights) and the number ofsuccesses (hardly the right word for a catheter blockage - the number ofblockages during the first 10 nights) is also 6.
The probability justcalculated is 'if there is no association between Nitrofurantoin and catheterblockages, what are the chances of getting 6 blockages in the 10 nights withoutNitrofurantoin?' It can also be calculated the other way round: what arethe chances of there being no blockage in 20 nights with Nitrofurantoin if lackof blockages is not associated with it? In this case, theprobability of success for a single trial is 20/30 = 0.6667 the number oftrials is 6 (the number of blockages on all 30 nights) and the number ofsuccesses (the number of blockages on the last 20 nights) is 0. Theanswer is the same, that is, probability = 0.0014.

Themultinomial distribution can also be used with 2 outcomes (blockage/ noblockage) probability of outcome 1 (blockage) is 10/30 = 0.3333; frequency ofoutcome 1 (number of blockages when not taking Nitrofurantoin) = 6; probabilityof outcome 2 (no blockage) is 20/30 = 0.6667; frequency of outcome 2 is 0 (thenumber of blockages when taking Nitrofurantoin). The answer is the sameas before (p = 0.0014).

This too can be calculated theother way round: outcome 1 (no blockage, probability 0.6667, frequency 0);outcome 2 (blockage, probability 0.3333, frequency 6) with the same result.

So for the 30 nights of the trial, it is possible to saythat taking Nitrofurantoin and catheter repositioning were associated withstopping my catheter blockages with only a very small chance of beingwrong (probability 0.0014) which is 1 chance in 714.

That was the situation on 13/8/16. It is changingevery day. If I have a blockage, the chances of the statement being wrongwill increase. If I do not have ablockage, the chances of the statement being wrong will become even smaller; forexample when the number of nights without a blockage reached 50 (12thSeptember), the probability became (10/60)6 = 0.16676 = 0.000021, that is 21 chancesin a million or 1 in 47,619 (one million is the number that 0.000021 would haveto be multiplied by to get 21).

Such probabilities as p = 0.0014 or p = 0.000021 do notpredict the frequency with which I can expect a blockage; neither do theypredict the proportion of patients with a condition the same as mine havingtheir blockages stopped. All theymean is that in my case, it is almost certain that taking Nitrofurantoin andrepositioning my catheter have reduced the chances of getting a blockage: p = 0.000021 (the probability of there not being an association) or 1-p =0.999979 (the probability of there being an association) are measures ofthe chance that Nitrofurantoin and catheter repositioning are associated withcatheter blocking; they are not measures of what that association is, thatis, how much they reduce the chancesof a blockage.

So for patients with a condition the same as mine, the treatment can be expected to reduce the frequency ofblockages for almost all of them.

It could be argued that although what has been calculatedshow a very strong correlation between taking Nitrofurantoin/catheterrepositioning and the absence of blockages, demonstrating correlation is notthe same as demonstrating cause: something else might have happened on 24thJuly 2016 when I started taking Nitrofurantoin regularly and it was this'something else' which stopped my blockages. This is true, but I am not aware of anything happening on that day orsoon after, and which has continued to be effective since then, which could bethis 'something else'.

It is possible to predict the number of blockages withinany specified period using the Poisson probability distribution:

For example, suppose we wish to predict the chance of 1blockage in a period of 7 days, the Poisson random variable would be 1. The average rate of success is the average numberof blockages which in the past have occurred in 7 days (number ofblockages/number of days in observation period x 7). To predict the chance of 2blockages in 28 days, the Poisson random variable would be 2 and the averagerate of success would be the average number of blockages in 28 days. As long as there are no blockages on nightsfollowing taking Nitrofurantoin, the average number of blockages for any periodis 0: so until there is a blockage, theprediction of future blockages for any period is zero.

NITROFURANTOIN AND BLOCKAGES 16th January 2016 to 16th January 2017

My first blockage occurred on the night of 16/17th January2016.

There were 23 blockages in the first 190 days, none in thefollowing 176.
If Nitrofurantoin and catheter repositioning had no effect,the probability of having 23 blockages in 190 days followed by no blockage in176 days is (190/(190+176))23 or 0.519123 = 0.0000002823 which is less than 3 chances in10 million (ten million is the number that 0.0000002823 would have to bemultiplied by to get 2.823).
The base is 0.5191 andthe exponent is 23.

The probability of Nitrofurantoin having had no effect isbecoming even smaller every day I do not have a blockage.

The binomial distribution can also be used with the sameresult:

where N = 23, k = 23, p = 0.5191 and the answer is p(kout of N)

The multinomial distribution can be used too:
where the number of outcomesis 2 (night/day), the number of occurrences 23 and 0, p = 0.5191 and 1- 0.5191= 0.4809.


Side-effects and build-up of bacterial resistance areconcerns about antibiotics generally. Although there are no indications that I have had either so far, I amnow trying to determine the minimum effective dose of Nitrofurantoin.

Having taken 50mg every day from 24th July until 22ndAugust (30 days), this was reduced to 3 or 4 times per week and then to justnights when I was feeling feverish as might warn of a urinary infection or whenthere was a considerable amount of sediment in my catheter:
August 24, 25, 26, 28, 29, 30;
September 1, 2, 4, 7, 8, 10, 13, 16, 18, 19, 22, 25;
October 1, 5, 6, 7, 11, 14, 15, 17, 20 (100mg), 21, 22, 23,25, 29, 31;
November 4, 5, 7, 10, 13, 16, 19, 22, 24, 26, 28;
December 1, 3, 5, 8, 11, 12, 17, 22, 31;
January 8, 16, 18, 22;
February 5, 13, 16, 20, 25;
March 11,


The Users' Information Leaflets issued by Dr Reddy'sLaboratories and Genfura recommend 50 or 100mg four times per day for sevendays for treatment of bacterial infections of the liver, bladder and otherparts of the urinary tract and 50mg or 100mg once per day at night for theprevention of further infections but do not say for how long. The connection between preventing infectionsand preventing catheter blockages is not mentioned. The leaflets list many possibleside-effects. So far, I have notexperienced any but others do; see for example:

Will it cease to be effective after a while? So far it hasn't. It has already provided me with a very welcomerelief from the misery of regular catheter blockages, possibly preventedinternal damage and saved a significant amount of nurses' time.

Brumfitt and Hamilton-Miller support the use ofNitrofurantoin for long-term (12 months) prevention of urinary infections:;see also and


Has the catheter had any influence on the occurrence ofblockages? There is a widely-held viewthat catheter production has lagged a long way behind the technology availableand is failing patients badly. See forexample:

I can refer only to the catheters I have had. My indwelling suprapubic catheter waspresented to me in hospital in May 2013 as being better than the intermittenturethral catheter used between January and May 2013. This would have been impossible on returninghome because I live alone and have very little movement in my hands. The indwelling urinary catheter via theurethra was not mentioned to me, presumably because the hospital consultantsthought it would be less suitable than the type I have got.

In my case, my present type of catheter is the onlypractical one I was offered. The threatof urinary infection is always with me. Hotand cold sweats occur most days. My armsare often stinging with cold while the rest of me, where I have sensation, isoverheating. It is possible that bettercatheters would render blockages something of the past, which would be welcomerelief for more than 200,000 people in the UK with long-term catheters and severaltimes as many when shorter-term users are included.

We may wonder why the enormous buying power of the NHSresults in some not-very-good equipment and medications at high cost while inthe commercial world, large organisations are able to use their buying power tosecure what the customer wants at competitive prices. An Internet search on NHS overcharged (1/2/17)revealed about 190,000 results for drugs:

and 143,000 for equipment: ed+equipment

The standard period between changes of catheter has been 12weeks (5 weeks in hospital) but there have been some variations. It was changed shortly before 11pm on 23/7/16by a night nurse attending a blockage and was followed less than 4 hours later bya blockage of the new catheter, described by the nurse as 'positional'. The catheter that was replaced coincided with more blockages thanany other I have had. I had no furtherblockage with the new catheter which was replaced on 18/10/16. In my case so far, there is no substantial evidenceconnecting blockages with particular catheters or with the period of time sinceinstallation ..... but absence of evidence is not evidence ofabsence.


Although Nitrofurantoin and catheter repositioning haveeliminated blockages so far, often there is sediment in my catheter: sosupporting methods are used to keep it clear:

1 High waterintake: widely recommended to wash out loose sediment and to dilute urine andbacterial concentration: possibly a necessary but not sufficient method toprevent blockages. It certainly did notcause the sudden cessation of blockages from 24/7/16.

2 Bladderwash-outs: I have never had a blockage on the night immediately following awash-out but I have had at least one on the night after that: they reduce butdo not eliminate blockages.

3 Loosening anysediment in the catheter by rolling it between the hands.

4 Adding vinegarto food seems to be followed by a clearer catheter (by lowering urine pH andacting as an antibiotic). There are manyother natural antibiotics which might help:

Drinking lemon tea has been followed by a clearer catheter. To make lemon tea, I simply cut an unpeeledlemon in half, slice or chop one half into pieces and pour hot water ontoit. In a small cup (200ml.) this can betopped up with hot water several times, squashing the lemon with a spoon.

It looks possible that the sediment was caused by reducingthe amount of Nitrofurantoin below 50mg per day and that the supporting methodsmight be alternatives to higher doses. Nitrofurantoin does appear to clear sedimentfrom the catheter not much longer than an hour after taking it - as would beexpected from its property of preventing blockages.

It seems likely that the bacteria killed by Nitrofurantoincreated the sediment which resulted in most of the blockages. Samples of the contents of the catheter atthe times of blockages would have been useful to test this.
Nitrofurantoin has been shown tobe effective against: Citrobacterspecies, Coagulasenegative staphylococci, E. coli, Enterococcusfaecalis, Klebsiellaspecies, Staphylococcusaureus, Staphylococcussaprophyticus, Streptococcusagalactiae
Observations point to one or more ofthese bacteria as the likely cause of perhaps three-quarters of my blockages (the other quarter being the result ofphysical obstructions). Without knowingwhich of these bacteria caused the blockages, we can not be sure thatNitrofurantoin is the most selective antibiotic to deal with them or what otherantibiotics would also work. Also, wedo not know at what pH the blockages occurred.
Many or all strains of the followinggenera are resistant to Nitrofurantoin: Enterobacter, Klebsiella, Proteus, Pseudomonas


The methods explained in this paper will be effective onlyfor blockages caused by certain types of bacteria or certain catheterpositions. It remains to be seen to whatproportion of catheter blockages these conditions apply. In July 2016, before taking Nitrofurantoin aspart of this treatment, a rehabilitation consultant suggested to me that kidneystones might be the cause of my blockages. Bits breaking off the stones would block the catheter. In the absence of any samples from mycatheter having been taken at the time of a blockage, this seemed a reasonablepossibility, but now that the blockages have been demonstrated to bebacteriological (otherwise they would not have been stopped by Nitrofurantoin)it looks unlikely in my case - but not necessarily in others.

After reading an earlier version ofthis paper in November 2016, a urology consultant suggested to me that mine mightbe a case of bladder stones because these can cause re-infection. Repeated infections, might in some cases, beprevented by removal of bladder stones.

The following are commonly mentionedsymptoms of bladder stones, not necessarily soon after their formation:
1 lower abdominal pain, 2 pain or discomfort when urinating, 3 difficultywhen starting or a stop-start in urinating, 4 cloudy or dark-colouredurine, 5 discomfort or pain in the penis, 6 urinating more frequently, especially at night, 7 bloodin the urine.

Spinal injury and consequent loss ofsensation and use of a catheter might reduceawareness of some of these symptoms. Cloudy urine is commonly mentioned but not sediment which would beneeded to cause a catheter blockage. Darkening of urine is also a usual consequence of taking Nitrofurantoin.

Anyone with persistent catheterblockages might be recommended by their medical practitioner to have acystoscopy, an examination of the bladder with a fine telescope, to detectwhether there are any stones. Stickler and Feneley suggest that Proteus mirabilis produced by bladder stones is a likely cause ofcatheter blockages:
However, Nitrofurantoin is noteffective against most strains of Proteus. See also

So Nitrofurantoin is unlikely to prevent blockages caused by bladderstones.


The nurses, particularly the nightnurses, have left me with the impression that catheter blockages are much morecommon than they need to be. Often, theyleft me with a cheery 'See you again soon'. The prevailing attitude in both the medical and nursing professions thatthey are an inevitable consequence of having a catheter should bequestioned.

In November 2016 I 'phoned the night nurses to thank them for coming to unblock mycatheter on 23 nights between January and July, to explain why I have notcalled them out since July, and to offer to send them a copy of this paper: 'Wedon't give out e-mail addresses over the phone'.
Meanwhile, patients wake in theearly hours of the morning, sweating profusely, trembling with massive shocksof spasms, resulting in urine being forced back to the kidneys and in extremecases, autonomic dysreflexia, internal damage and death. Night nurses rushbetween patients to unblock catheters which do not need to be blocked.Sometimes they have taken over 2 hours to reach me (although the average isabout 1 hour 20 minutes), explaining that they have had a lot of patients withblocked catheters that night.
Recently, a nurse from the localhealth authority called to assess my condition. A friend who was with mementioned my catheter blockages and offered her this paper: no thanks. 'It'ssomething they can live with'.
Although I have not heard anyone elsesay so explicitly, 'something they can live with' reflects the prevailingattitude of others connected to the nursing and medical professions. With a few exceptions, no-one wants to knowand the few who do want to know are not in positions to persuade the medicaland nursing professions to listen to a patient.
Such has been the resistance to anapproved dose of an approved medication. How much greater can we expect the difficulties of improvement in themedications available for spasms for example, or equipment such as catheters,when those needing them have been conditioned to expect nothing better thanwhat they are given, when manufacturers are allowed to happily continue to sellthe same old products. I must say I amleft wondering whether the brick wall of complacency about catheter blockagesalso applies to other treatments and equipment that those with spinal injuriesneed - including treating the injury itself - and beyond spinal injuries.

This, of course, is my ownstory. My need for a catheter was causedby breaking my neck at C4/5 with consequent spinal damage and paralysis belowmy shoulders. I do not know for how manyothers the treatment would be effective but I have no reason to believe thatit would not work for some of those -male or female - with catheters for other reasons. Other people might need different doses ofNitrofurantoin. If you have persistentblockages or know someone who has, do consider showing this paper to a medicalpractitioner.

P.S. Still no blockage since the night of 23rd / 24th July.

20th March 2017